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pharm
2/19/98
happy birthday to me.
kotlikoff


Glucocorticoids

widely used, widely abused.

starting with some review 
from biochemistry *ARGH*!!
concentrating on physiological release of 
corticosteroids
metabolic effects of endogenous or synthetic 
glucocorticoids
then we'll discuss specific drugs, and finish up with 
some clinical touchstones regarding appropriate and inappropriate use and 
unwanted effects and complications.

p 1 of handout

adrenal cortex 
releases gluco- and mineralo- corticoids as well as sex steroids. the 
glucocorticoids and mineralocorticoids are the "salt and sugar" hormones. 
an animal that's adrenalectomized can live, as long as it gets 
appropriate food, water, and salt. the adrenal allows for accomodation of 
environmental fluctuation - without it, periods of starvation, lack of 
salt, too much salt, etc are not tolerated, and result in death. so they 
call it the "freedom organ."

Addison, in 1855, recognized a naturally 
occuring symptom of adrenal destruction, aka Addison's dz, or 
hypoadrenocorticism.

aldosterone wasn't isolated til the 50s. then 
cortisone was discovered in the late 40s, and had a dramatic effect. this 
was a miracle drug for those with rhemumatoid arthritis or other 
autoimmune diseases. led to a nobel prize within two years. Since that 
time, glucocorticoids have had a kind of a reputation clinically as being 
a kind of miracle drug. however,they also have a history of complications 
and inappropriate uses.

first figure on p 1 - somewhat review, but 
critical to understand use of glucocorticoids. 

you have the typical 
hypothalamic-pituitary-adrenal axis associated with glucocorticoid 
release. that is to say, in the hypothalamus, a variety of stimuli 
converge to control release of CRF corticotrophin releasing factor. not 
just biochemical stimuli, but also environmental influences associated 
with stress, starvation, oncoming danger, etc. these stimuli are 
processed by the brain, and result in regulation of release of CRF. CRF 
stimulates release of ACTH from the pituitary gland. ACTH once released 
stimulates adrenal cortical cells to make cortisol. not to release 
preformed cortisol, but to start synthesising it, and then to release it. 
so the system works like this. cortisol has a fairly rapid half life. so 
there's minute to minute/hour to hour regulation of cortisol levels. 


feedback mechanisms: cortisol levels are sensed in the pituitary gland, 
and regulate release of ACTH. this is the classic negative feedback, 
where excess cortisol results in decreased ACTH release, less cortisol 
synthesis, etc. at the same time, cortisol also feeds back to the 
hypothalamus to decrease release of CRF. this process is under normal 
diurnal regulation. for diurnal mammals, cortisol levels rise in early 
AM, at the approach of daylight, as the animal begins activity and faces 
environmental stresses. they fall somewhat during the day, and in the 
evening, as the levels are not required. it is this normal fluctuation 
that is mimicked or that we attempt to mimic with exogenous 
administration - we try to mimic that AM increase in cortisol with a 
single dose in the AM. cats are naturally not diurnal, so their cortisol 
levels are way more variable. 

again, there is a critical 
hypothalamic-adrenal-pituitary axis. This is important. without ACTH 
release, even though you have a normal adrenal gland, you will not have 
sufficient cortisol synthesis and release. ACTH is required for adrenal 
cortical cells to make cortisol. most critical: cortisol level in plasma 
is sensed in pituitary which regulates ACTH release and in hypothalamus 
which regulates CRF release.

Cushing described hyperadrenocorticism - 
excess cortisol. this can be an iatrogenic problem as well. but cushing 
was describing a common cause of hyperadrenocorticism, which is pituitary 
dependent - too much ACTH stimulation. adrenal is normal. so, say, a 
functional pituitary adenoma may result in excess release of ACTH and 
failure of the negative feedback mechanism. when this occurs, it's 
clinically similar to having an adrenal adenoma making excess cortisol. 
bottom line is, there is too much cortisol being made.

therapeutic uses 
of these compounds - 

ACTH: does this have a therapeutic use? not 
really. it has problems associated with administration - it's a peptide, 
and may provoke autoimmune responses. also promotes both gluco and 
mineralocorticoid release, which isn't always desired. however, it's used 
diagnostically in the ACTH stimulation test, which tests release of 
cortisol from adrenal in response to a dose of ACTH. you give the ACTH, 
which should stimulate the adrenal cortex to release cortisol. then you 
measure the response to the ACTH, to see if adrenal is making too much, 
or not enough cortisol. this works out to testing if adrenal is too big 
or too small. 

dexamethasone: conversely, looking again at this limbic 
pathway, another common clinical/diagnostic test is to inject 
dexamethasone, for the dex suppression test. this is a test where you 
inject dexamethasone and measure cortisol. if negative feedback works, 
pituitary should sense the dexamethasone, decrease ACTH release, and 
decrease endogenous cortisol release. so this tests the pituitary gland, 
and can help you to detect a pituitary adenoma, loss of ability to detect 
cortisol level in plasma. 

now, we're looking at some biochem related 
stuff. the biochemistry of glucocorticoids is rather critical for 
understanding differences b/w exogenous and naturally occuring steroids. 


ACTH stimulates the adrenal cortex to start a synthetic pathway. the ACTH 
receptor stimulates increase in cAMP, which activates enzymes, and the 
synthesis of these steroid hormones from cholesterol occurs. so, there 
are three major pathways - mineralocorticoids, of which aldosterone is 
the physiological hormone; the glucocorticoids, represented by cortisol 
and corticosterone in man and domestic animals - cortisol being the 
principal compound in man, dog, horse, pig, cat, and corticosterone in 
rabbit, mouse and rat. the main difference is corticosterone has a 
shorter half life in the blood, which makes a difference in terms of 
physiologic regulation. so, you trigger synthesis of cortisol or 
corticosterone - both of which have glucocorticoid and mineralocorticoid 
activity - and aldosterone, which has mainly only mineralocorticoid 
activity, due to a modification on a side chain.  the synthesis of 
cortisol is regulated by many enzymes - mixed function p450 enzymes, and 
there are a couple of structural features of these molecules - 
glucocorticoid activity requires a C at C21 - this is also seen in 
aldosterone but aldosterone ahs another molecule on it limiting 
glucocorticoid activity. also, the double bonds in these steroids are 
reduced in the liver - they're glucoronidated, and eliminated by the 
kidney. this is important b/c the compounds we use exogenously are often 
modified at the double bond region to decrease the ability of the liver 
to reduce the double bond - often they add a fluorine atom or something 
to stabilize the bond - and this slows the elimination of it, changing 
the halflife of the synthetic steroid. 

ok. 
we know that 
corticosteroids are made on demand, not stored, have short half life, and 
are largely protein bound. they are metabolized in the liver, reduced and 
conjugated - the double bond at C4-5 is the main target for that 
metabolism. synthetic analogues have changes there that slow the 
metabolism. 

so.
how do the glucocorticoids work on their target cells? 
it's known that there are a superfamily of steroid receptors that have 
structural similarities - the glucocorticoid and mineralocorticoid and 
estrogen and progesterone receptors resemble those for vitamin D and 
retinoic acid. these are cytosolic receptors that bind this family of 
molecules which can then alter protein expression. 

the steroid 
receptors, one member of the superfamily, is a cytosolic receptor that 
binds cortisol, translocates it to the nucleus, binds DNA, and acts as a 
transcription factor to alter the level of protein expression - either 
inducing expression of a protein, or decreasing expression of a protein. 
so they are either positive or negative transcription factors. these are 
ligand dependent transcription factors. one key element, one key family 
of proteins that are induced by this steroid/cortisol receptor complex 
are lipocortins - lipocortin inhibits phospholipase A2. 

so remember - 
antiinflammatory effect of glucocorticoids is dependent on protein 
synthesis for its major action - inhibition of phospholipase A2 via the 
lipocortin production. 

phew, that actually makes sense!

slide: 
structure of cortisol. carbon at C21, C4-5 double bond - you don't have 
to know specific carbon atom structure function things, but you should 
know ** it is important ** that there is an alteration in the structure 
of cortisol that results in an increased in halftime of elimination for 
the exogenous steroids. have some sense of activity relationships whereby 
you increase glucocorticoid activity with some structural changes and 
mineralocorticoid activity with other structural changes.

slide: 
structure of hydrocortisone and exogenous glucocorticoids that you will 
administer, that are altered but have similar structures to cortisol. the 
fluorine atoms are present in longer acting glucocorticoids 
(triamcinolone), not in shorter acting ones (prednisolone), but they 
share the same cortisol backbone. modifications confer clinical 
advantages like longer activity, lower mineralocorticoid activity.


metabolic effects of endogenous cortisol (and exogenous cortisol):


glucocorticoids are "sugar hormones" and a way to remember many of the 
metabolic effects is to think of them as hormones that evolved to 
preserve glucose dependent functions - kind of like insulin, in the sense 
of allowing animal to adjust to different dietary intake and survive 
periods of starvation. so think of the metabolic effects in terms of: 

effects on CHO - mainly gluconeogenesis. 
effect on fat - increase in fat 
deposition (net storing of energy as fat). effect on protein - catabolism 
- breaking down protein to make sugar (substrate for gluconeogenesis and 
fat storage)

look more closely at CHO - gluconeogenesis occurs from 
increased liver glycogen deposition, increased liver glucose production 
from protein breakdown. liver catabolizes protein, to make glucose - to 
preserve glucose levels in the plasma. this glucose production also 
increases levels of insulin. this results in a somewhat of a 
hyperglycemia - a mild hyperglycemia. 

the hallmarks of these effects on 
CHO metabolism, with *excess* glucocorticoids (cushing's dz, 
hyperadrenocorticism, or excessive use of these drugs) would be more 
prominent hyperglycemia and increased insulin requirement, that can 
precipitate diabetes in animals with marginal pancreatic function. 


effects on fat are more complicated - there's inhibition of glucose 
uptake by fat cells, which results in some lipolysis within fat cells, 
but the increase in insulin stimulates lipogenesis, leading to increased 
fat deposition in certain areas. this is characteristic of cushings - 
increased fat in characteristic areas of the body - in people, a moon 
face and buffalo hump; in animals, often a pendulous abdomen. think JFK- 
he had addison's dz, was treated with exogenous glucocorticoids, and 
developed a moon face. 
sometimes this is called centripedal fat 
accumulation - it's in the truncal regions of the body. classical 
cushinoid dog with pendulous abdomen, and thin little legs. truncal 
obesity is a sign of excessive glucocorticoids.

protein - catabolism can 
be quite important clinically. with cushings one sees thin skin, loss of 
haircoat, muscle wasting, weakness - this contributes to the classic 
appearance of the cushinoid dog. this is, again - one can think of this 
as shunting glucose from protein, maintaining glucose dependent 
functions. this also results in steroid myopathy in people, a common loss 
of muscle associated with long term glucocorticoid administration.


effects on electrolytes and water are also important. cortisol and 
corticosterone have mineralocorticoid effects. the exogenous ones have 
less, but still some. aldosterone increases sodium reabsorption in distal 
tubule, increasing potassium and H+ excretion. this results in net 
increase in body water. hyperadrenocorticism causes an increase in total 
body sodium and total body water. this can lead to edema fluid 
accumulation in lungs and abdomen. you have increased cardiac load. 


addison's dz, a decrease in cortisol, will result in lower sodium, 
increased potassium. this decreases extracellular fluid volume, can cause 
circulatory collapse and renal insufficiency. 

so - now we talked about 
the normal targets of cortisol and the effects of exogenous cortisol in 
terms of metabolism. these effects we've discussed aren't the desired 
effects - we don't want to produce truncal obesity or hyperglycemia - we 
want to reduce inflammation! but these other effects occur also, there is 
no separation of antiinflammatory effects from metabolic effects. all the 
steroids are binding to the same receptor having the same cellular 
effect. 

Antiinflammatory effects and immunosuppressive effects:

most 
important therapeutic effects of glucocorticoids are on the phospholipase 
A2 pathway we discussed before - principally this effect is on peripheral 
white cells. these cells are critical amplifiers of this immune response. 
they take recognition of foreign protein, parasite, or whatever, and 
recognize it, amplify local response, resulting in release of LTB4 which 
calls in other inflammatory cells, and LTC4 and D4, and the prostenoids, 
which have local effects that we recognize as the classic inflammatory 
effects. they have effects on peripheral cell distribution:
they cause a 
neutrophilia - they prevent the neutrophils from exiting into the tissue. 
they prevent margination and diapedesis of neutrophils into the tissue. 
this is a common stress response - stress neutrophilia - due to increased 
cortisol level. 
also cause a marked lymphocytopenia, by preserving 
lymphocytes in spleen and LNs, decreasing movement into the blood. 
they 
decrease eosinophils and basophils, too.

effects on cell function 
generally are through the phospholipase A2 pathway. lipocortin is induced 
by the steroid/receptor complex which acts as transcription factor in the 
nucleus. by virtue of this effect at the very top of the arachadonic acid 
cascade, by ability to inhibit prostaglandins and leukotrienes, they are 
very potent antiinflammatory compounds, more so than NSAIDs. 


glucocorticoids require nuclear transcription. they require a new protein 
synthesis, or decrease in protein expression. principally, synthesis of 
lipocortin, for antiinflammatory effects. 

platelets are sensitive to 
NSAIDs because they require thromboxane A2 for normal function. however, 
glucocorticoids have no effect on platelets - because platelets have no 
nucleus. they have enzymes - but no nucleus. a steroid can't affect the 
platelet because it can't induce transcription. it has no effect on the 
preformed compounds in the platelets. steroids don't work directly on 
phospholipase A2 - they have to induce the expression of lipocortin to do 
that. 

again: platelet is a piece of the cell. has membrane 
phospholipids and all required enzymes. when it is activated, 
phospholipase A2 liberates arachadonic acid, cyclooxygenase produces 
thromboxane A2, platelet gets sticky. steroids do nothing to this - they 
can't make lipocortin since there is no nucleus. but, drugs that inhibit 
cyclooxygenase (NSAIDs) prevent breakdown of of arachadonic acid into 
thromboxane by cox.

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backing up for a minute: the 
structure/activity relationships are always a problem, because if you try 
to fully explain it, it's too much detail, and if you don't fully explain 
it, it's hard to understand. you do not need to know the details. you 
*should* know that there are changes in the activity and structure of 
cortisol vs aldosterone that account for the different physiological 
effects, and that there are changes of structure in synthetic steroids 
that make them metabolized more slowly so they last longer, and this is 
associated with a fluorine added to a double bond. that's what you need 
to know. the third thing is that these activity differences b/w 
glucocorticoids and mineralocorticoids are also targeted by synthetic 
compounds, to make compounds with very very little mineralocorticoid 
activity and a lot of glucocorticoid activity. that is what you need to 
know about that.

another question - difference b/w glucocorticoids and 
corticosteroids - terms are often misused. glucocorticoids are 
corticosteroids that have glucose metabolizing activity - they have the 
effects on gluconeogenesis, fat deposition, and catabolism, without the 
mineralocorticoid activity. now, sometimes people say they're using 
corticosteroids when they mean glucocorticoids. aldosterone is a 
corticosteroid too. 

back to antiinflammatory and immunosuppressive 
effects-

remember - we talked about having the binding to some receptor 
in the cytosol, translocating to nucleus, producing lipocortin, 
inhibiting phospholipase A2 - this is the underlying mechanism for the 
antiinflammatory action. now, the antiinflammatory effects are mainly on 
peripheral leukocytes, but there are other effets - vascular effects: 
somewhat overrated. people in clinics discuss steroids increasing patency 
of the vasculature, maintaining BP, etc - this is usually due to the 
decreased inflammation, not really due to the alleged vascular 
stabilizing effects of the glucocorticoids.  immune suppression: at high 
doses, glucocorticoids have immunosuppressive effects byond the 
antiinflammatory effects. high doses are used with autoimmune dz, to 
suppress Ag/Ab recognition and cellular immunity. sometimes used in organ 
transplant patients. these are higher doses than the antiinflammatory 
range. now, there is some overlap of course. so if you are immunizing an 
animal, can you give glucocorticoids for inflammation? yeah, you can by 
and large promote the desired immune response, if you're using lower, 
antiinflammatory doses. if you're giving a high dose, no, you probably 
won't immunize effectively.

slide: points out many cell mediated 
interactions associated with mphage/APC showing Ag to T cell, producing 
Ab response - cytokines are produced,etc- these things are generally all 
inhibited by high doses of glucocorticoids.

now - moving from endogenous 
cortisol into the steroids you will use clinically - lets talk about 
those.

as stated, all the synthetic glucocorticoids have both the good 
antiinflammatory effects and the undesirable metabolic effects. 
however,there are advantages to the exogenous ones in two respects: 


one, they have less sodium retention activity than cortisol. normalizing 
cortisol activity to 1, aldosterone has 3000. triamcinolone, 
betamethasone, etc have virtually no sodium retention activity. 
the 
antiinflammatory effects, however, correlate very closely with liver 
glycogen deposition - these can't be separated out. prednisolone is 4x as 
potent as cortisol in antiinflammatory effects, but also in metabolic 
effects! this is important. people say "use steroid x because it's more 
potent." you have to remember, all that means is that you can prescribe a 
smaller pill. you can give fewer mg to get the same effect. BUT the 
effect will be the same! you can give 4x more potent pred, or give a 
bigger pill of cortisol. the physiological result is the same. it doesn't 
matter which you give.

the main advantage, is a decrease in 
mineralocorticoid activity in synthetic compounds. the other advantage is 
that we can change the duration of action in synthetic compounds - short, 
medium, or long acting. 

cortisol/hydrocortisone - assign values of 1.

pred, methylpred, short acting
triamcinalone intermediate
betamethasone, 
dexamethasone - long acting

these drugs exhibit differences in duration 
of action, salt retaining activity. prednisolone, prednisone have less 
mineralocorticoid activity, but still have some, and that's why animals 
get PU/PD on pred. then you can switch to say, methylpred, which has less 
salt retaining property. 

again - stressing the point of equivalent oral 
dosage - if you see an ad that says "use dexamethasone, it's 25 times 
more potent than cortisol, you only have to give 0.75 mg of dex instead 
of 20 mg of cortisol," think about this. you'd have to use 6x as much 
pred as dexamethasone. but, 6x as much pred is a lot cheaper than the 
equivalent amount of dexamethasone. so you might as well use pred. there 
is no reason to use a smaller amount. potency just means you give a 
smaller pill. 

formulations, clinical uses of these compounds:

these 
drugs come generally as water soluble and non water soluble.

water 
soluble:

can be used IV
usually Na+ phosphate esters, Na+ succinate 
esters eg pred Na succinate
when you give them, the phosphate or 
succinate dissociates off, leaving free steroid.
when you have the free 
steroid, the length of time you have the steroid on board depends on how 
strong that double bond is and how long it takes the liver to 
glucuronidate it and conjugate it and eliminate it. pred: 1/2 hr; 
triamcinolone, 5-6 hrs; dexamethasone, 10-12 hrs.

non water soluble:


can't be used IV
usually complexed with acetonide or acetate - eg 
triamcinolone acetate
these are called "repositol steroids"
it doesn't 
matter what the steroid base is. they are given IM, injected into tissue, 
and the complex b/w the acetonide or acetate and the steroid breaks down 
really slowly - making it long acting, ultra long acting. as the acetate 
comes off, the steroid is freed, and becomes available. the rate limiting 
thing is how long it takes for the compound to break down. once the 
steroid is released, elimination depends on the steroid base. but even a 
pred-based substance will be ultra long acting if it's in this kind of 
formulation.

principles of therapy:

we divide steroid therapy into 
short term or long term. the first thing is, say you have a situation 
where you know you have to give glucocorticoids for 3 days, and that's 
all. eg, for acute back trauma, where rapid dosing with glucocorticoids 
decreases loss of neural function associated with injury. so this animal 
will get short term therapy - less than three days. anything over three 
days is long term. 

short term:
less than three days.
will want to use 
injectable or oral compound that's long acting. we know tht if we use 
steroid for 3 days or less we'll have no long term effects on metabolism 
or adrenal function. we won't cause adrenal atrophy, because it's only 
three days. we won't have longterm metabolic effects. so you use a water 
soluble compound, probably long acting, because it's easier. one 
injection a day, or one pill a day, for three days. a good choice might 
be dexamethasone sodium phosphate. give IV or orally. long acting - once 
daily dosing. not ultralong acting! you could give pred twice a day, 
also. either way. 


long term:
more than three days of treatment
you 
want to do alternate day therapy with a short acting compound - this is 
your ideal. you don't want to use a long acting steroid in this 
situation. you want to not totally inhibit the 
hypothalamic-pituitary-adrenal axis. so you give a short acting steroid 
every other day. usually you start, give an increasing dose daily til 
signs are suppressed, then double that dose and give it every other day. 
drug of choice is usually pred - short acting, cheap. this allows the 
adrenal gland on the alternate day to see no exogenous pred, so it's 
stimulated to function. this helps to prevent atrophy of adrenal cortex 
which would occur in the absence of ACTH stimulation.
now - why do you 
double the dose that you need to suppress signs? well, you're changing 
the dosing interval. you give a big jolt, suppress inflammation, then by 
the second day as signs are returning, you give a second dose. this 
really helps to prevent iatrogenic addison's dz/adrenal atrophy, and 
minimizes iatrogenic cushing's signs. biggest cause of failure of this 
mode is failing to double the dose when you move to EOD administration.


in many animals in many clinical situations, it's difficult to use this 
ideal method. owners may not be able to pill cats, people may forget to 
give pills, or whatever. so some people require an easier regimen. then, 
you would go to using repositols. this is where one would say "ok, i'm 
going to inject a compound that I know will be there for 2-5 weeks. see p 
8 of handout. depo medrol and vetalog are two common repositols. these 
drugs decrease ACTH response for as long as 5 wks. the point is, once you 
inject this stuff, it's there. the problem occurs when maybe the clinical 
signs recur before a month is over, and the owner wants another 
injection. then you don't know how much is on board, and the adrenal 
gland gets no vacation. for repositols - never give more than once a 
month, and avoid them if possible. 

ideally - have dex sp for rapid iv 
use, pred pills, and some repositol lying around.

it's very important to 
remember the difference b/w water soluble and non water soluble 
compounds.

therapeutic indications for glucocorticoid use:

allergic 
reactions, collagen vascular disorders that are autoimmune associated, 
eye dz like anterior uveitis, allergic conjunctivitis choroiditis; GI dz 
such as IBD; blood dz,  often immune mediated; sometimes in infections 
may use glucocorticoids to control excessive inflammation, as in septic 
shock, where increased vascular permeability due to endotoxin is a huge 
problem- but not necessarily useful in hypovolemic shock although they 
are used anyway, with little clinical rationale; inflammatory conditions 
of bones and joints; neurological disorders and neuro trauma - important 
to use rapidly post trauma; transplants; pulmonary dz - inflammation, 
asthma esp feline asthma; renal diseases eg nephrotic syndrome; skin 
disorders, and other things.

complications of therapy - in handout:

iatrogenic hyperadrenocorticism, adrenal insufficiency following 
withdrawal (this is why it is important to taper off chronic steroids), 
unmasking of preclinical diabetes mellitus, nervousness, mood changes, 
pseutotumor cerebri, cataracts common w/iatrogenic cushings, 
pancreatitis, ulceration, hepatopathy, growth retardation, hyperglycemia, 
generalized catabolism, osteoporosis, myopathy, wasting, weakness, 
urticaria, calcinosis cutis, laminitis in the horse, abortions in 
pregnant bovines.

note: these drugs do not treat underlying dz, only 
stop inflammation. don't be lulled into false sense of security.

quick 
summary:

I. HPA axis - feedback regulation is critical and pivotal to 
understanding clinical use of corticosteroids. must know role of ACTH, 
how ACTH release is regulated and how it regulates cortisol synthesis. 
remember that dex, pred, triamcinolone will all suppress the HPA just 
like endogenous cortisol.

II. biochemistry (argh). ACTH--> increased 
cAMP in cortical cells -->synthesis of cortisol.  also remember 
structure/function relationship - see above (way above) - three main 
things are glucocorticoid activity, mineralocorticicoid activity, and 
rate of elimination - all relate to structure. remember that things are 
reduced and conjugated in liver, and eliminated by kidney.

III. 
mechanism of action - binding receptor, going to nucleus, inducing 
protein - remember why it won't work in platelets. receptor is important. 
metabolic effects are important. gluconeogenic, catabolic, truncal fat 
storage. also antiinflammatory effects. remember phospholipase A2, 
lipocortin, effects on neutrophils. 

IV. important differences b/w 
formulations - gluco/mineralo potency, duration of action

V. 
preparations - water vs non water soluble - remember this. you'll use it 
every day - phosphate/succinate vs acetate/acetonide
remember short 
term/long term paradigm - see above. 

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